COHERENT ELECTRON-TRANSPORT IN SUPERCONDUCTING-NORMAL METALLIC-FILMS

We study the transport properties of a quasi-two-dimensional diffusive normal metal film attached to a superconductor. We demonstrate that t he properties of such films can essentially differ from those of quasi -one-dimensional systems: In the presence of the proximity-induced sup erconductivity in a sufficiently wide film, its conductance may not on ly increase but also decrease with temperature. We develop a quantitat ive theory and discuss the physical nature of this effect. Our theory provides a natural explanation for recent experimental findings referr ed to as the ''anomalous proximity effect.''